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<html>
  <head>
    <meta charset='utf-8'>
    <meta name='viewport' content='width=device-width, initial-scale=1, user-scalable=no'>
    <meta name='mobile-web-app-capable' content='yes'>
    <meta name='apple-mobile-web-app-capable' content='yes'>
    <link rel='icon' type='image/png' sizes='32x32' href='favicon-32x32.png'>
    <link rel='icon' type='image/png' sizes='96x96' href='favicon-96x96.png'>
    <link rel='stylesheet' href='css/common.css'>

    <title>Immersive Viewport scaling</title>
  </head>
  <body>
    <header>
      <details open>
        <summary>Viewport scaling</summary>
        <p>
          This sample demonstrates how a session can request to render to
          a smaller area of its layer. This can be used to dynamically
          lower the number of pixels that need to be rendered. This can
          help experiences that are fragment bound for a short amount
          of time.
          <a class="back" href="./">Back</a>
          <br/>
          Use projection layer: <input id='useLayer' type='checkbox'/>
        </p>
      </details>
    </header>
    <main style='text-align: center;'>
      <p>Click 'Enter XR' to see content</p>
    </main>
    <script type="module">
      import {WebXRButton} from './js/util/webxr-button.js';
      import {Scene, WebXRView} from './js/render/scenes/scene.js';
      import {Renderer, createWebGLContext} from './js/render/core/renderer.js';
      import {Gltf2Node} from './js/render/nodes/gltf2.js';
      import {SkyboxNode} from './js/render/nodes/skybox.js';
      import {QueryArgs} from './js/util/query-args.js';

      import WebXRPolyfill from './js/third-party/webxr-polyfill/build/webxr-polyfill.module.js';
      if (QueryArgs.getBool('usePolyfill', true)) {
        let polyfill = new WebXRPolyfill();
      }

      // XR globals.
      let xrButton = null;
      let xrRefSpace = null;

      // WebGL scene globals.
      let gl = null;
      let renderer = null;
      let scene = new Scene();
      let scale = 1;
      let scale_down = true;
      let useLayerCheckbox = document.getElementById('useLayer');
      let useLayer = false;
      // layer support
      let xrGLFactory = null;
      let xrFramebuffer = null;
      let proj_layer = null;
      let count = true;

      scene.addNode(new Gltf2Node({url: 'media/gltf/space/space.gltf'}));
      scene.addNode(new SkyboxNode({url: 'media/textures/milky-way-4k.png'}));

      function initXR() {
        xrButton = new WebXRButton({
          onRequestSession: onRequestSession,
          onEndSession: onEndSession
        });
        document.querySelector('header').appendChild(xrButton.domElement);

        if (navigator.xr) {
          navigator.xr.isSessionSupported('immersive-vr').then((supported) => {
            xrButton.enabled = supported;
          });
        }
      }

      function onRequestSession() {
        useLayer = useLayerCheckbox.checked;
        return navigator.xr.requestSession('immersive-vr', {
          requiredFeatures: useLayer?['layers']:[],
        }).then(onSessionStarted);
      }

      function onSessionStarted(session) {
        xrButton.setSession(session);

        session.addEventListener('end', onSessionEnded);

        gl = createWebGLContext({
          xrCompatible: true, webgl2: true
        });

        renderer = new Renderer(gl);

        scene.setRenderer(renderer);

        if (useLayer) {
            xrFramebuffer = gl.createFramebuffer();
            xrGLFactory = new XRWebGLBinding(session, gl);
        } else {
            let gllayer = new XRWebGLLayer(session, gl);
            gllayer.fixedFoveation = 1.0;
            session.updateRenderState({ baseLayer: gllayer });
        }

        session.requestReferenceSpace('local').then((refSpace) => {
          xrRefSpace = refSpace;

          if (useLayer) {
            proj_layer = xrGLFactory.createProjectionLayer({ stencil: false });
            proj_layer.fixedFoveation = 1;
            session.updateRenderState({ layers: [proj_layer] });
          }
          session.requestAnimationFrame(onXRFrame);
        });

        session.onselectstart = () => {
          count = false;
        }
        session.onselectend = () => {
          count = true;
        }
      }

      function onEndSession(session) {
        session.end();
      }

      function onSessionEnded(event) {
        xrButton.setSession(null);

        renderer = null;
      }

      function onXRFrame(t, frame) {
        let session = frame.session;

        scene.startFrame();
        scene.updateInputSources(frame, xrRefSpace);

        session.requestAnimationFrame(onXRFrame);

        let pose = frame.getViewerPose(xrRefSpace);

        if (pose) {
          if (useLayer) {
            let views = [];
            for (let view of pose.views) {
                view.requestViewportScale(scale);
                let subImage = xrGLFactory.getViewSubImage(proj_layer, view);
                subImage.framebuffer = xrFramebuffer;
                let viewport = subImage.viewport;
                gl.bindFramebuffer(gl.FRAMEBUFFER, xrFramebuffer);
                gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, subImage.colorTexture, 0);
                gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT, gl.TEXTURE_2D, subImage.depthStencilTexture, 0);

                views.push(new WebXRView(view, subImage, viewport));
            }
            scene.drawViewArray(views);
          } else {
            let glLayer = session.renderState.baseLayer;

            gl.bindFramebuffer(gl.FRAMEBUFFER, glLayer.framebuffer);

            gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

            for (let view of pose.views) {
                view.requestViewportScale(scale);

                let viewport = glLayer.getViewport(view);
                gl.viewport(viewport.x, viewport.y,
                            viewport.width, viewport.height);

                scene.draw(view.projectionMatrix, view.transform);
            }
          }

          if (count)
            scale += scale_down ? -0.004 : 0.004;

          if (scale >= 1) {
            scale = 1;
            scale_down = true;
          } else if (scale <= 0.125) {
            scale = 0.125;
            scale_down = false;
          }
        }

        scene.endFrame();
      }

      initXR();
    </script>
  </body>
</html>
